The invention generally concerns a method of determining mining progress in open cast mining using satellite geodesy.
For the purposes of ascertaining the geodetic position of a point, that is to say the co-ordinates in respect of length, width and height of that point, by means of satellite geodesy, in principle at least four satellites are required. The signals emitted from the satellites can then be simultaneously received by a receiver which corresponds to the point whose geodetic position is to be ascertained. The co-ordinates of that point are ascertained by a procedure in which the distance from that point to three of the satellites is detected, with the transit time, that is to say the difference in terms of time between the time at which the transmitted signals are emitted and the time at which the transmitted signals are received being used in order to ascertain the distance between the above-mentioned point and the respective three satellites. As however the satellites on the one hand and the receiver on the other hand have different time measurement systems, the fourth satellite referred to above is necessary to adapt and correct the time measuring systems and thus determine a reference time. That ensures that the actual signal transit times can be properly ascertained. As the respective co-ordinates of the satellites are known, the co-ordinates of the receiver at the point whose position is to be determined can be clearly ascertained from the respective distances and the time correction effect referred to above.
The Global Positioning System (GPS) which is being built at the present time, in the United States of America, is for example suitable for satellite geodesy purposes. That system is planned to have at least 21 navigational satellites disposed around the earth in such a way that it is possible to take a bearing on and communicate with at least four satellites simultaneously from any position on the earth at any time.
At the present time, when ascertaining co-ordinates of a point by means of satellite geodesy, a level of accuracy of .+-.10 meters can be achieved in terms of absolute positional measurement, that is to say if the co-ordinates of a point are ascertained directly from the measured distances. That deviation is due in particular to the fact that the transmission signals from the satellites, in the from of electromagnetic waves, in travelling towards the earth, must pass through different media which cause the ways to suffer deviation in different ways due to refraction, while having different influences on the transit time thereof. It is therefore desirable to provide a further receiver which is disposed in the vicinity of the point whose co-ordinates are to be ascertained, with the co-ordinates of the further receiver being known. By means of what is known as the differential measurement process, it is then possible for the influences, which cannot be foreseen and which cannot be calculated, of the different media on the nature of wave propagation, to be eliminated as it is to be assumed that the signals travel along approximately the same paths to the respective receivers. When using that measurement procedure, it is possible at the present time to achieve a degree of accuracy of about .+-.0.01 meter. In that connection reference is made to WO 87/06713, to the disclosure and content of which attention is expressly directed for the incorporation thereof into this specification.
The intervals between two co-ordinate determining operations, using satellite geodesy, depend inter alia on the speed of operation of the computer system which evaluates and assesses the signals received. Depending on the computing output, the measurement intervals involved may be for example only one second. Short co-ordinate ascertainment times of that nature permit the positions of moving items of equipment to be almost continuously ascertained.
The invention seeks to make it possible to use the procedure for ascertaining co-ordinates of a point with a relatively high degree of accuracy and with short measurement intervals by means of satellite geodesy, for the purposes of determining the co-ordinates of the extraction device of a travelling large-scale extraction apparatus, for example the position of the bucket wheel of a bucket wheel digger or excavator which is used in open cast mining. In such equipment, the bucket wheel which represents the extraction device for mining purposes is carried by a jib which is generally mounted to a travelling support structure of the digger or excavator, in such a way that the jib is pivotable in an at least substantially vertical plane. For the sake of simplicity, reference will generally be made hereinafter to a bucket wheel excavator, without however the principles of the present invention being restricted thereto.
In regard to operating open cast mining, the results of the operation in regard to the materials produced as well as the current topography of the open-cast mining are factors of especial significance. To carry out an open cast mining procedure, that generally involves producing a model of the deposit to be mined, indicating the arrangement of the individual layers in the deposit, the thicknesses thereof and so forth. On the one hand, the layers in the deposit are those which contain the usable material, for example coal, brown coal or lignite or the like, and on the other hand layers which cover over or are interposed between the layers of the usable material and which must be removed in order to be able to mine the layers of usable material. By reference to that model of the mining terrain, and by virtue of a comparison between the initial situation thereof and the current topography of the deposit, it is possible to find out what amounts of which materials have already been removed and where. In other words, the current topography of the open cast mining operation is always reproduced by virtue of such a comparison procedure. Hitherto manual measurement and surveying procedures have been the usual practice for ascertaining the materials which have been mined, in regard to the amount, position and nature thereof, so that, because of the relatively large amount of time involved in doing that, a precise plan can be drawn up and the model of the open cast mining deposit can be updated for example only once per week.
The publication `Moderne Technologien und Entwicklungen im Markscheidewesen`, Clausthal-Zellerfeld Jubilee Colloquium, May 14th/15th, 1986, issued October, 1986, pages 177 ff, describe possible ways of using satellite geodesy to arrive at automatic ascertainment of the location of a bucket wheel digger or excavator and the bucket wheel thereof in order in that way, by way of the current topography of the open cast mining procedure, to arrive at balance sheets in respect of the materials involved, to provide information about the materials which have already been mined and about the materials which are still present in the deposit. Reference is also made therein to the production of a model of the deposit, which is to be subdivided in such a way as to give addressable cubes of a size of about 4.times.4.times.4 meters. In that respect it is correctly assumed that, wherever the position of the bucket wheel of the excavator was located, there can no longer be any material at that point in the deposit. The tests described in that publication however only concerned basically settling the question of whether a receiver or the antenna thereof, which is disposed on the bucket wheel excavator jib, permits sufficiently accurate continuous positional detection of the antenna, while the bucket wheel excavator is in operation. It was not possible in those tests to test practical usability as the necessary requirements for the purpose was lacking.
Even if the receiver or the antenna thereof could be mounted on the bucket wheel, and it will be appreciated that that cannot be the case as the bucket wheel rotates during the extraction operations, that would not give any information about the position of the bucket wheel which would be sufficiently accurate to permit conclusions to be drawn about the materials which have been mined. Bucket wheels of modern bucket wheel excavators are of a very large size in three-dimensional terms. For example the diameters thereof may be more than 20 meters. In other words, even if the receiver could be mounted on the bucket wheel, it would only be possible to ascertain the co-ordinates of a point at the bucket wheel, which however does not give any information whatsoever about the position and orientation of the bucket wheel. That knowledge however would be necessary in order to be able to ascertain in what region the bucket wheel had already removed material from the deposit, especially as there are only ever certain areas of the periphery of the bucket wheel which are in engagement with the deposit.
It will be appreciated that the above-described disadvantages really make themselves felt when the receiver is mounted on the jib at a spacing from the extraction device, that is to say for example at a spacing from the bucket wheel. In addition the large dimensions of the bucket wheel mean that the receiver or the antenna thereof must be disposed at a relatively large distance from the bucket wheel as otherwise, depending on the position of the jib carrying the bucket wheel and therewith also the position of the bucket wheel itself, there is the possibility of the bucket wheel moving into a position in which it is disposed between the antenna and at least one of the satellites, so that it effectively screens the antenna from the satellite. It would then no longer be possible for signals from that satellite to be received. Although the distance which is therefore required between the receiver or the antenna thereof and the bucket wheel is fixed, in this case also it is not sufficient to ascertain the position of the receiver in order to calculate therefrom the position of the bucket wheel itself, as knowing only the co-ordinates of the point corresponding to the antenna also does not make it possible to arrive at any conclusion about the three-dimensional orientation of the jib. However knowledge of that jib orientation is a necessary aspect in order to be able to determine the position and orientation of the bucket wheel of the excavator.